Parthenogenesis doubles the rate of amino acid substitution in Whiptail mitochondria

Sexual reproduction is ubiquitous in the natural world, suggesting that sex must have extensive benefits to overcome the cost of males compared to asexual reproduction. One hypothesized advantage of sex with strong theoretical support is that sex plays a role in removing deleterious mutations from the genome. Theory predicts that transitions to asexuality should lead to the suppression of recombination and segregation and, in turn, weakened natural selection, allowing for the accumulation of slightly deleterious mutations. We tested this prediction by estimating the dN/dS ratios in asexual vertebrate lineages in the genus Aspidoscelis using whole mitochondrial genomes from seven asexual and five sexual species. We found higher dN/dS ratios in asexual Aspidoscelis species, indicating that asexual whiptails accumulate non-synonymous substitutions due to weaker purifying selection. Additionally, we estimated nucleotide diversity and found that asexuals harbor significantly less diversity. Thus, despite their recent origins, slightly deleterious mutations accumulated rapidly enough in asexual lineages to be detected. We provided empirical evidence to corroborate the connection between asexuality and increased amino acid substitutions in asexual vertebrate lineages.有性生殖在自然界中普遍存在，这表明相较于无性生殖，有性生殖必然具备诸多演化优势，以抵消雄性个体带来的繁殖成本。现有理论强力支持的有性生殖优势假说之一，便是有性生殖能够清除基因组中的有害突变。理论预测，向无性生殖的演化转变会导致重组与分离过程受到抑制，进而削弱自然选择作用，使得基因组中轻微有害突变得以积累。本研究通过分析Aspidoscelis属无性生殖脊椎动物支系的dN/dS比值（dN/dS ratio），所用数据来自7个无性物种与5个有性物种的完整线粒体基因组，以此验证上述理论预测。研究发现，Aspidoscelis属的无性生殖物种具有更高的dN/dS比值，这表明由于纯化选择作用减弱，无性生殖鞭尾蜥积累了更多非同义替换。此外，本研究还对核苷酸多样性进行了估算，发现无性生殖支系的核苷酸多样性显著更低。因此，尽管无性生殖支系的起源时间较近，但其基因组内的轻微有害突变仍以足够快的速度积累，可被实验检测到。本研究提供了实证证据，证实了无性生殖脊椎动物支系中，无性生殖与氨基酸替换频率升高之间的关联。